Accelerator for the vulcanization of rubber



Patented Nov. 17, 1931 UNITED-STATES PATENT FFICE;

'e oEeE STAFFORD wHITBY, E MONTREAL, QUEBEQCANADA, .AS'sIeNoE, EYnEsN-E ASSIGNMENTS, To THE EOESSLER & HASSLACHER GHEIVIICALECOMPANELOF N W YoE'K, N. Y., A CORPORATION oEn LAwnRE AcoELEEAToE, FOR THE voLoAnIzATIoNoE niiBEEn' a aw n Ap qai l n file ijq t b raa 92 This invention relates to vulcanizing rubber or similarniaterials, and to theproducts obtained thereby being moreparticularly directed t'o acceleration of vulcanization by an ,5 organic accelerator and to the products resultingf-rom such vulcanization.

The object of-this invention is to produce an accelerator of the vulcanization of rubher which will, when properly compounded,

,19 produce 'finished'r'ubber articles-of superior physical properties such as high stress strain relationship, increased tensile strength, and freedom from sulphuring out or blooming. Further it is desired to provide high powered 1 5 accelerators at lower costs than are now prev- .alent. v v

An v acceptable accelerator of rubber vulcanization should have'several characteristics. It-should'beof low cost; it should be 2. completeinitself, i. errequire 11 additional agents or activators; it should be applicable to stocks utilizing various rubber substitutes,'antioxidants, conditioners, etc. utilized by rubber compounders; furthermore,

2,5 itshould "have suitable physical characteristicsfit should preferably be ays'olid hav ing a melting point belowthe vulcanization temperature at whichit'is to be used, but sufficientlyhigh so that the accelerator will not fuse or lump" together at ordinary tenl if peratures, itshould be practically odorless;

it should give of]? no fumes having an irritating action on the.eyes,.' nose, and throat as or deleterious to the health of theioperator 7.5, Theacceleratorf of my invention fulfills these conditionsl My accelerator belongs to a general class of substances which I call carbalkoxythione disulphides and which are 40 represented by the general formula My accelerator is the isopropyl'derivative,

Serial No. 228,101. .Rae mtmr 24,1931.

h fo mula 2.

, .1 on-oeors-u ltis tube seen from theaboveformnlathat this compound isa CSQderivativeofa secondary" alcohol, namely, isopropyl alcohol, two of'the simple CS5 derivatives of the alcohol being-condensed to .give my accelerator. 1 Iain aware that it has beenpreviously proposed to utilize/disulphides Similar in structure-to the above which, however, are derivatives. of primary alcohols. I have'foundthat my derivative ifrom the isopropyl alcohol forms a superior accelerator; Itis complete in itself and requires no activators, such as amines, to secure very high tensiles in'the finished rubber. .Itcal'lrbeyusedin conjunction with the ordinary rubber conditioning agents, antioxidants, rubber substitutes, reclairngjet'c. or incombination with other acceleratorslif desired." None ofthese'are' necessary, new.

ever, as will be'seen'from the examples given below. 'I have-found that thecorresponding derivatives of the primary alcohols do v not give satisfactory results unless an amine ac"- tivator" is utilized. Furthermore, accelerator is a solidhaving satisfactory melting point from the standpointof packing, storage, and use in the rubber the accelerator,

being solid, can be obtained in highgpurity';

this is impossible with the normally liquid or extremely low melting derivatives. The

carbisopropoxy thione disulphide and has utilize NaOCl in a process as described by G. C. Bailey in his copending application S. N. 17 5,633, filed March 15, 1927. If chlorine is used in the oxidation considerable impurities are formed and the product is usually liquid. Furthermore, especially valuable stress-strain relationships and general adaptability are found with this accelerator,

which do not occur with the primary alcohol derivatives as seen from the'examples given below.

. This isopropyl compound when utilized as the accelerator in rubber vulcanization by incorporating it with unvulcanized rubber or the like, and in the presence of a vulcanizing agent gave results as follows:

The above ingredients were thoroughly mixed on the rubber mill and then cured at the temperature of 40 lbs. steam for 60 minutes. A test piece from this rubber gave a stretch of 710%; a load at 600% elongation of 3000 lbs/in. and a-tensile strength at break of 37 69 lbs./in. average hardness 60 with a Shore durometer.

XmPLE II Highly compounded stock Brown crepe 9.0 Smoked sheet 91.0

Reclaim 10.0 Sulphur 1 73.8 Zinc oxide 14.0 Carbon black 30.0 M. RLX. 5.0

Hard wood pitch 1.0 Carbisopropoxy thione disulphide 2.5 Low melting formaldehyde aniline 0.5

. The above stock was cured at a temperature of 20 lbs. steam and the results as given below were obtained: I

Z58. pressure 7 I Load at fj jf Stretch 500% Tensile Hardness 1 p .1 Elong. I 1

so 740 2800 a 5450 i 00. 45 72o 2400 5520 so so. 720 Y 2000 5200 so My accelerator has another distinct advan- 05 tage in that it has a sharp critical time and temperature. For this reason up to a very definite temperature no prevulcanization or setting up will occur and when vulcanization is started the cure is quickly set 011 and the rubber reaches its maximum tensile in a short period of time, and then has afiat tensiletemperature curve. This is shown by the following example.

EXAMPLE III Critical temperature test Standard low zine stock V Carbisopropoxy thione disulphide 1 I ,7 Time of cure 1 hour.

S P Stretch Set fig-Z Tensile 100 No vulcanization. 105 700 10 600 2519 110 801 15 1550 i 4638 115 841 10 1180 4627 121 860 15 900 3986 141 930 15 500 2415 Orz'tz'eal time test The stock of this example was now cured at a temperature of 115? C. for varying periods and results obtained. as given below.

Cure Stretch Set 932; Tensile 25 Practically no vulcanization- 28 vulcanization just commenced-too weak to test.

30 821 15 1200 610.9 40 802 20 1200 4660 Y 50 822 15 1200 .4880 821 p 20. 1150' f 4615 810 20' 1250 4490 From Example III, it is seen that at 100 C. no vulcanization was obtained in 1 hour;

at C. fair vulcanization was obtained, '12::

and at C. the 'maximum had been reached. Raising the temperaturebeyond this point was somewhat detrimental to the action of the accelerator although it could V be safely used up to 120 C.

The optimum cure is seen to have occurred in 30 minutes at C., or a temperature corresponding to that of steam at 10 pounds pressure. Beyond 30 minutes through 75 minutes the tensile fell off only very gradually. An interesting feature of the test of Example III is the constancy of the load at 600% elongation. a J Claims: 7

1. Process of treating rubberor similar material which comprises incorporating with unvulcanized rubber or the like a vulcanizing agent and carbisopropoxy thione disulphide and subjecting the mixture. to a vulcanizing temperature.

2. Process of accelerating the vulcanization of rubber which comprises vulcanizing the same in the presence of the oxidation product of the CS derivative of isopropyl alcohol. 5 3. A vulcanized rubber derivedfrom rubber or similar material incorporated with a, vulcanizing agent and carbisopropoxy thione disulphide.

Signed at Perth 'Amboy, in the county of Middlesex and State of New Jersey this 14th day of October A. D. 1927.

GEORGE STAFFORD WHITBY. 

